The Labor Party is watching these developments with extreme concern as some of its federal MPs believe that faith-based voters reacted adversely to its reproductive rights proposals at the last federal election. Historically Labor has also been identified as the major party more closely associated with reproductive rights reforms. It has also been subject to fiercer internal battles as it has attempted to contain religiously inspired philosophical differences among its members. The latter has now lessened as the party has become more secular.

But it is the Coalition, holding government in both the federal and NSW spheres, which is most threatened by internal divisions because of intense controversy inspired by conservatives, mostly religious, within the Liberal and National parties. While the NSW abortion decriminalisation legislation has been brought forward by a cross-party group of MPs, it is the Coalition which is effectively being held responsible for both that state legislation and federal freedom of religion legislation.

Political life is immersed in deeply held and fiercely fought values and beliefs originating in various social and political philosophies. But history shows that none threaten the unity of political parties as much as those, like abortion law reform, which touch on intensely held religious beliefs. Australian political history is littered with threats of possible splits within parties and efforts by parties to find procedural and policy compromises to avoid such splits.

This is one reason why the political history of abortion law reform since the 1960s in Australia has departed from the most common parliamentary practice in which the government of the day moves its own bills which are then voted on along strict party lines.

Instead abortion law reform, like other sexual morality/life and death issues, is usually the subject of a private members bill with free or conscience voting for all MPs as is currently the case in NSW. This process means that individual MPs have much more freedom to vote as they wish than is usually the case. But the wider community consequently has much greater opportunity to lobby MPs, who don't have the usual party policy protections to hide behind.

The controversy in NSW should be viewed in this context. It features all the usual ingredients: a private members bill, intense lobbying of MPs and ultimately threats by Coalition MPs to leave the party, most notably by Tanya Davies, the MP for Mulgoa and Kevin Conolly, MP for Riverstone.

This lobbying of MPs has had many features, including both powerful elites and community-based events. Strong statements by high-profile church leaders, including Anglican Archbishop Glenn Davies and Catholic Archbishop Anthony Fisher, have accompanied many street protests at which pro-life protesters have clashed with defenders of the bill. It has even featured the active intervention in state politics by the federal member for New England and former deputy prime minister, Barnaby Joyce.

There are clearly many links between state and federal Coalition politics in this area. Freedom of religion and abortion politics share many of the same networks inside and outside of Parliament. Religious conservatives generally not only oppose abortion decriminalisation but also want tougher freedom of religion legislation. While they have some Labor party links most of their contacts are with the Coalition parties.

These religious conservatives only have the support of a minority of public opinion, demonstrated by public opinion polls and by their failure in the 2017 same sex marriage postal plebiscite. They are undeterred, however, because they are driven by the deeply held belief that their position is right.

They are also strategically placed and their strongest support, up to 50 per cent or more in certain electorates and sectors, lies mostly within the Coalition parties and Coalition supporters in the community. This gives them leverage within the party rooms and in party branches. It extends not just to the traditional and evangelical wings of the mainstream Christian communities, but also to newer immigrant and ethnic Christian churches and to culturally conservative non-Christians, including the Muslim community.

These are disruptive issues for all political parties, but especially for the Coalition. In the short term they may damage Gladys Berejiklian and Scott Morrison, even cause their downfall, as conservatives wage internal guerrilla warfare and refuse to take no for an answer even when the majority advocates a different direction.

The main general political lesson is that intensity of belief, not just numbers, matters in politics, because those who are willing to take radical steps to leverage their beliefs can magnify their impact. Threatening to leave your party altogether and to move to the crossbench, like Davies has, is a big, and probably career-ending, step. Even threatening to cross-the-floor on one issue alone is extraordinarily brave (in the political sense).

There are also lessons for other policy areas and for the other side of the ideological divide. Progressives should learn from the way conservatives fight their battles to the bitter end. Progressive causes too need individuals who are ready to sacrifice their careers to advance that cause. Think Indigenous constitutional recognition, climate action, international aid and development, asylum seekers and refugees and poverty eradication. More MPs should be willing to cross the floor and even as a last resort to abandon their party altogether for the right cause.